Panchromatic is a very lightweight application which produces a simple monochrome line drawing of any image file. By reducing an image to only a handful of colours Panchromatic can draw lines where any two colours meet.
It uses a very simple interface and in a couple of clicks you can turn any image into a sharp outlined bitmap. There are a few modes, selected with a single mouse click, to cater for different image content. Choose between silhouette, multi coloured and multi-toned to get the sharpest outline possible. The size and colour of the outline can be configured as well as the background colour.
It should be able to pick out any strong shapes in an image. Use it pick out shrimps, boxing gloves, toes, lampshades, whatever you've got a picture of, give it a whirl in Panchromatic. If you've got loads of free time why not stick the image through Whitenoir (the sister app) first!
For best results it's best to start with a bmp, png or any other lossless type of image compression. If all you've got is a jpg then Panchromatic will still use it but the result may be on the haggered side. The transformation can be quite intensive - especially if your camera uses tons of mega pixels - so if you find it's taking a second or two you might find it better to reduce your image size first - but only if you're impatient.
I have no doubt this can be achieved in Photoshop, GIMP et al, but I'm just too lazy to find out how.